Process for recovering concentrated acetic acid from dilute acetic acid



H. SUIDA March 10, 1931.

PROCESS FOR RECOVERING CCNGENTRATED ACETIQ ACID FROM DILUTE ACETIC ACIDmud Fob. 16, 1928 Wafer and fleet/c field Mixture;

Patented 10, 1931 UNITED STATES PATENT OFFICE HERHANN some, or momma,AUSTRIA PROCESS FOR RECOVEBING CONCENTBATED ACET'IC ACID FROM DIIIUTEACE'IIC ACID Application filed February 16, 1928, Serial No. 254,895,and in Austria July 1.4, 1927.

In Patent N0.1,621,441 a process for the recovery of concentrated aceticacid from d1- lute' acetic acid is dlsclosed, which consists inconducting a homogeneous or anic solvent or concentrating agent, insolule or difficultly soluble in water and boiling point higher than that 0acetic acid, in counter-current to the superheated yapours of water andacetic acid, recovermg the concentrating agent containing the aceticacid in the concentrated condition and-se arating the mixture in knownmanner by 'stillatlon into the acid-free concentrating agent andconcentrated acetic acid.

In the aforesaid patent a series of various types of solvents orconcentrating agents are given by wa of-example which are suitable foruse in t e. process. Chief among these solvents are phenols whichexhibit good concentrating powers in respect of acetic acid.

In so far vas the concentrating agents are volatile to a limited extentwith water vaours, losses of the same due to their soluility indischarge water result, and these losses must be recovered from theacetic acidfree discharge water.

I have found that the esters of cyclical, particularl Y polybasiccarboxylic acids which exhibit very high boiling points, eat

80 stability anda very slight volatilizability, possess excellentconcentrating powers in respect of dilute acetic acid, and that theseesters may therefore be employed primarily .where tar-free acetic acidvapours are to be concentrated, that is, for exam le, in thereconcentration of the discharge rom the cellulose acetate manufacture.Thus, for example, the methyl, ethyl and butyl esters of the nahthene-acids or the analogous esters of ort ophthalic'acid exhibitexcellent concentrating powers. Therewith the losses resulting due tothe volatilizability with water vapour and the solubility in water,particularly of the esters with'higher alcohols, are

. 4 so slight that a considerable technical ad- Vance is attained bytheir use. For example orthophthalic acid dibutyl ester boils at 310320C. and the solubility of this ester in water is 'less than one gram ofthe ester '50 in one liter of water.

ossessing a The following examples and the annexed drawing serve toillustrate the process of this invention:

1. Dilute, for example per cent, acetic acid is passed through a pipe 1into a still 2 and is vaporized by means of a coil 3. The vapors passthrough the pipe 4 into the lower part of a column 5 charged withfilling material, such as rings or the like, a heating tube 6 extendingaxially of said column. A steam coil 9 in the column 5 above the outletof the pipe 4 serves to super-heat the acetic acid-- water-vapormixture. orthophthalic acid dibutyl ester is allowed to flow into theupper part of the column 5 through a pipe 7. Thus while one art ofdilute acetic acid is passed in vapor orm from the pipe 4 through thecolumn, 1 to 2 parts of ortho hthalic acid dibutyl ester aresimultaneous fy fed in liquid form into the upper part 0 he column.

'The column 5 is extended below the outlet of the pipe 4 and its lowerportion is maintained at a temperature of150 C. in known manner by meansof the heating coil 9. Water vapor'practically free from acetic acid 1leaves the upper part of the column through a pipe 11 and carries withit practically none of the solvent. The mixture of orthophthalic aciddibutyl ester, charged with 15-30% of concentrated acetic acid, flowsout from the lower portion of the column through the siphon tube 8. Theresulting mixture is separated in known manner for example bydistillation in a vacuum apparatus, into concentrated acetic acid andacid-free orthophthalic acid dibutyl ester.

2. The operation is carried out in the same manner as in Example 1 usingorthophthalic acid dihexyl ester as solvent and kee in the proportionsof dilute acetic acid an so vent about the same. For the concentrationuse is made of a column, such as 5, to the upper part of which theorthophthalic acid dihexyl ester is fed, as througlithe pipe 7, whilethe vapours of dilute acetic acid are fed into a lower part of thecolumn from a vaporizer, such as 2, and fiow upwardly through thecolumn. In the lower part of the column the solventcharged with aceticacid collects, provision being made for heating the lower part of thecolumn to a temperature of 15Q-155 C., as by means of a coil 9. Themixture on leaving-the column through a syphon tube, such as 8, isseparated in known manner into 5 the orthophthalic' acid dihexyl'esterand concentrated acetic acid. In the case the water vapours freed fromthe acetic acid pass away, as through the ipe 11, without carrying ofiany trace at a l of solvent. The vapours may be condensed and led away.The acetic acid obtained is of 95 to 99% concentratlon depending uponthe temperature maintained at the lowest endv of the'column.

3. Technical ethyl esters of naphthene acids can be employed in place oforthophthalic acid'dibuty ester in a similar manner as described forxample 1, or in the place of orthophthalic acid dihexyl ester as used inExample 2.

Use may, however, also be made of even higher boiling, esters of'phthalic acid, for example esters of heptyl alcohol or the neutil'alesters of glycol and of glycerine inter WhatI claim is: Y

1. A process for recovering concentrated acetic acid from dilute aceticacid, consist-- ing in bringing a superheated acetic acidwater va ormixture in direct contact with a counterow of a'liquid ester formed bythe,

- chemical union of a cyclical carbox lic acid with an aliphaticalcohol, whereby t e acetic acid is extracted from the mixture, and thenseparating the resulting solution into concentrated acetic acid and acidfree ester.

2. A process according to claim 1, in which the ester therein isreplaced by a liquid ester of a polybasic cyclical carboxylic acid.

3. A process according to claim 1, in which b the ester therein isreplaced by a liquid ester formed by the chemical union of a polybasiccyclical carboxylic acid with a monohydroxy aliphatic alcohol. v i v 4.A process according to claim 1, in which the ester therein is replacedbya liquid ester formed by the chemical union of-an orthophthalic acidwith an aliphatic alcohol.

5. A process according to claim 1 in which the ester therein is replacedby orthophthalic dihexylester.

In testimony whereof-I have hereunto set In hand. y HERMANN SUIDA.

